Similar known devices maintain the gap between the sealing faces of the stationary and rotating ring by means of hydrodynamic forces which are produced by the friction of the fluid film against the surfaces of the ring geometry.
The rotating ring of the conventional dry seal is fabricated from a hard ceramic material with spiral grooves etched into its sealing surface. The stationary ring of such device is fabricated either from a soft carbon or a hard ceramic material with a smooth sealing surface. Geometrically the adjoining surfaces of the rings are shaped conically.
When motionless, the stationary ring is pressed against the rotating ring by the tension of springs. The full contact of both sealing faces minimizes the fluid leakage. While in motion, the grooves on the surface of the rotating ring perform a sweeping action against the fluid film. By virtue of the fluid viscosity the pumping action of the grooves builds up a pressure with a resulting force counteracting the spring tension. An equilibrium of force is accomplished with a tight spacing between the sealing faces.
The "lift off" of the stationary ring should under normal operating conditions occur at low rotational speeds. However, due to pressure or temperature deformation of sealing rings, fluid contaminants and the wear of sealing O-rings, occasional touching of the seal faces during rotation occurs. As an immediate consequence an abrasion associated with a heat buildup is a common cause of the seal damage.
Disorder in the delicate adjustment of the seal components may also cause uncontrolled vibrations with damaging effects.
Sensitivity to contaminants, requirement for the precision of components and flawless functioning of sealing rings are the main disadvantages of the described seals. In addition to the lack of robustness the seals exhibit undefined behaviour at very low rotational speeds and the rotation reversals.
It is therefore an object of the present invention to provide a robust, contact free seal that obviates or mitigates the above disadvantages.
In one aspect of the invention there is provided an improvement in a rotating machine having opposed spaced rotating and stationary sealing means, the rotating sealing means being attached to a rotating shaft and the stationary sealing means being fixed in relation to the housing of the machine, the rotating and stationary sealing means being separated by a fluid, the improvement comprising:
first sensing means for sensing the separation of the rotating sealing means from the stationary sealing means and for providing a sealing gap clearance signal indicative of the separation; and
first controlling and actuation means responsive to the sealing gap clearance signal for automatically and continuously controlling the separation of the rotating and stationary sealing means.
The improvement may comprise:
second sensing means for detecting contact of the rotating sealing means with the stationary sealing means and providing a contact signal indicative of contact; and
relay means for relaying the contact signal to the first actuation means for automatically separating the rotating sealing means from the stationary sealing means upon the detection of the contact between them.
The improvement may further include the actuation means being pneumatically operated and being normally pressurized to maintain a constant separation of the rotating and stationary sealing means and the relay means including a solenoid responsive to the contact signal to relieve the pressure from the actuation means.
In several embodiments of the second sensing means, it could be a friction switch, an electrode contact switch or an hydraulic pressure sensor.
Preferably, the first controlling and actuating means includes a controller disposed to receive sealing gap clearance signals from the sensing means and at least one actuator responsive to the controller, and the controller is set to actuate the actuator only when the sealing gap clearance signals indicate a separation that deviates from a predetermined position.
There is preferably a plurality of sensing means (including the first sensing means) for sensing the separation of the rotating sealing means from the stationary sealing means and for providing respective sealing gap clearance signals indicative of the separation; and a plurality of controlling and actuation means responsive to the respective sealing gap clearance signals for automatically and continuously controlling the separation of the rotating and stationary sealing means. Each of these plurality of sensing means and the plurality of controlling and actuation means is distributed evenly around the stationary sealing means.
In another aspect, the invention provides a mechanism for maintaining a suitable spacing between the rotating and stationary components of a seal for fluid substances in a rotating machine having a shaft and a housing, the mechanism comprising:
rotating and stationary sealing means for providing spaced interfacing bodies between the rotating shaft and the housing;
sealing gap measuring means for providing a sealing gap clearance signal indicative of the spacing between the rotating and stationary sealing means;
controlling means responsive to the sealing gap clearance signal for maintaining a suitable spacing between the rotating and stationary sealing means; and
means responsive to the controlling means for moving the stationary sealing means in relation to the rotating sealing means.
In another aspect, the mechanism includes a sealing surface touch detecting means for perceiving and providing an alarm signal indicative of physical contact between the rotating and stationary sealing means and surface contact preventing means responsive to the alarm signal for separating the rotating sealing means from the stationary sealing means.
In a still another aspect, the invention includes the rotating sealing means being a ring shaped body having a first outer edge and further includes a ring member attached to the shaft adjacent the rotating sealing means, the ring member having a second outer edge; and a flexible membrane secured between the first outer edge of the rotating sealing means and the second outer edge of the ring member.
In a still further aspect, the stationary sealing means includes a circular stationary sealing ring fitted closely onto a stationary holding ring.
In a still further aspect, the stationary sealing ring is capable of an angular displacement in respect to the position of the stationary holding ring, and may include resilient means for holding the stationary sealing ring in a preset position in relation to the holding ring.
The sealing gap measuring means may include fluid jetting means in fluid connection with a fixed flow restricting means for establishing a hydrodynamic pressure commensurate with the spacing between the rotating and stationary sealing means.
The invention also provides a method of sealing a rotating machine having opposed spaced rotating and stationary sealing means, the rotating sealing means being attached to a rotating shaft and the stationary sealing means being fixed in relation to the housing of the machine, the rotating and stationary sealing means being separated by a fluid, the method comprising:
sensing the separation of the rotating sealing means from the stationary sealing means;
providing a sealing gap clearance signal indicative of the separation; and
automatically and continuously controlling the separation of the rotating and stationary sealing means using first controlling and actuation means responsive to the sealing gap clearance signal.
The method may also include detecting contact of the rotating sealing means with the stationary sealing means and providing a contact signal indicative of contact; and
relaying the contact signal to the first controlling and actuation means for automatically separating the rotating sealing means from the stationary sealing means upon the detection of the contact between them.
The method may also include adjusting the separation of the rotating and stationary sealing means only when the sealing gap clearance signals indicate a separation that exceeds a predetermined range.